Red vein in goldfish's tail, koi's tail
When I bought it, the goldfish's tail and koi's tail are all clear.
I quarantined these fishes. After like 3 weeks, I saw the red vein on the tails of goldfish and koi.
Since I saw these red vein, I continue keeping these fishes in the quarantine tank with salt. There is time I used paraguard and melafix as well.
They have been in my quarantine tanks for over 2 months. The temperature is getting colder and I am unable to put them in my Koi pond.
Is this really a disease? The fish with number 3 is in a separate tank, and it has more red vein than other fishes in other tanks.
Are they contagious?
Can the colder weather cause these? My area temperature lately around 50- 55 degree at night for the last 30 days.
Please help me, I really want to put these fishes into the pond before the winter. I have 10 other fishes in the pond right now. I don't want them to get this disease if it is contagious.
Please see it in the attached picture. I circled the red vein.
Thank you very much for your help.